Enhanced micro/nano-tribological performance in partially crystallized 60NiTi film
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Enhanced micro/nano-tribological performance in partially crystallized 60NiTi film Wanjun HE, Qunfeng ZENG* Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, Xi’an Jiaotong University, Xi’an 710049, China Received: 14 May 2020 / Revised: 23 August 2020 / Accepted: 10 September 2020
© The author(s) 2020. Abstract: The microstructure, mechanical and micro/nano-tribological properties of the 60NiTi film annealed at different temperature were investigated. The results reveal that annealing as-deposited 60NiTi film at 300, 375, and 600 °C for 1 h leads to structural relaxation, partial crystallization and full crystallization, respectively. Compared with the structurally relaxed structure, the partially crystallized structure exhibits increased hardness but decreased elastic modulus. This is because that the elastic modulus is reduced by Voigt model while the hardness is improved by composite effect. Due to the highest hardness and ratio of hardness to elastic modulus (H/E), the partially crystallized 60NiTi film has the lowest penetration depth and residual depth (i.e., groove depth). Besides, the results also reveal that ductile plowing is the dominant wear mechanism for all the annealed 60NiTi films. Under the condition of the ductile plowing, coefficient of friction and wear resistance are related to penetration depth and residual depth, respectively. Therefore, the partially crystallized 60NiTi film shows the best tribological performance at the micro/nano-scale. The current work not only highlights the important roles of hardness and H/E in improving the micro/nano-tribological properties but also concludes an efficient and simple method for simultaneously increasing hardness and H/E. Keywords: 60NiTi film; partial crystallization; micro/nano-friction; hardness; ratio of hardness to elastic modulus
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Introduction
With the application of precision mechanical system expanded, the demand for system of high reliability and minimized dimension is growing [1, 2]. This demand has stimulated the research on design and fabrication of micro/nano-electromechanical systems (MEMS/NEMS). The mechanical component of MEMS/ NEMS undergoes relative motion at the micro/nanoscale, which can result in friction and wear at the interface [3−8]. These interfacial phenomena are the cause of deterioration and complete failure of MEMS/ NEMS [9, 10]. Therefore, decreasing the friction and wear at the interface is essential. However, the application of liquid lubricant to MEMS/NEMS is limited due to its relatively high viscosity. Besides,
solid lubricant is also inappropriate for improving the tribological performance of MEMS/NEMS because solid lubricant can hardly be maintained and repaired after it is worn out during operation. Hence, it is necessary to develop an alternative, such as protective film, to effectively protect the mechanical component from premature wear and excessive friction. Materials for high tribological performance require high hardness (
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